The immune system has evolved specifically to detect and eliminate foreign or new material from a host. This material may be of viral, bacterial, or parasitic origin and may reside outside or within the cells of the host, or be of neoplastic origin.
The immune response to antigen is generally either cell mediated (T-cell mediated killing) or humoral (antibody production via recognition of whole antigen). The pattern of cytokine production by TH (T-Helper) cells involved in an immune response can influence which of these response types predominates: cell mediated immunity (TH1) is characterized by high IL-2 and IFNγ but low IL-4 production, whereas in humoral immunity (TH2) the pattern is low IL-2 and IFNγ but high IL-4, IL-5, IL-10. Since the secretory pattern is modulated at the level of the secondary lymphoid organ or cells, pharmacological manipulation of the specific TH cytokine pattern can influence the type and extent of the immune response generated.
The TH1-TH2 balance refers to the interconversion of the two different forms of helper T cells. The two forms have large scale and opposing effects on the immune system. If an immune response favors TH1 cells, then these cells will drive a cellular response, whereas TH2 cells will drive an antibody-dominated response. The type of antibodies responsible for some allergic reactions is induced by TH2 cells.
Vaccination is the best known and most successful application of immunological principles to human health. Naturally, to be introduced and approved, a vaccine must be effective and the efficacy of all vaccines is reviewed from time to time. Many factors affect vaccine efficacy. An effective vaccine must: induce the right sort of immunity; be stable on storage; and have sufficient immunogenicity. With non-living vaccines, in particular, it is often necessary to boost their immunogenicity with an adjuvant. This can also apply to some live, e.g., attenuated, vaccines. An “adjuvant” is a substance that enhances the immune response to an antigen.
During work in the 1920s on the production of animal antisera for human therapy, it was discovered that certain substances, notably aluminum salts, added to or emulsified with an antigen, greatly enhance antibody production, i.e., they act as adjuvants. Aluminum hydroxide is still widely used with, for example, diphtheria and tetanus toxoids.
GB-A-1 377 074, corresponding to U.S. Pat. No. 3,792,159, describes a process for preparing coprecipitates of tyrosine having an allergen dispersed therein.
GB-A-1 492 973, corresponding to U.S. Pat. No. 4,070,455, describes a process for preparing coprecipitates of tyrosine having a modified allergen dispersed therein. The allergen is modified by treatment with an agent, such as glutaraldehyde, which causes intra-molecular cross-linking and reduces the allergenicity of the product relative to the unmodified allergen.
3 De-O-acylated monophosphoryl lipid A (3-DMPL) is known from GB-A-2 220 211, corresponding to U.S. Pat. No. 4,912,094 and assigned to Ribi Immunochem. Res. (“Ribi”), now Corixa Corporation (Hamilton, Montana). Chemically, 3-DMPL is a mixture of 3 de-O-acylated monophosphoryl lipid A with 4, 5 or 6 acylated chains and is manufactured by Ribi Immunochem. Montana. A preferred form of 3 de-O-acylated monophosphoryl lipid A is disclosed in International Patent Publication No. WO 92/16556.
International Patent Publication No. WO 98/44947 describes a formulation for use in desensitization therapy of allergy sufferers that comprises an optionally modified allergen, tyrosine and 3 de-O-acylated monophosphoryl lipid A.
Considerable efforts have been made to produce better adjuvants, particularly for T-cell-mediated responses, but it should be stressed that very few of these more recent adjuvants have been accepted for routine human use.
It appears that the effect of adjuvants is due mainly to two activities: the concentration of antigen in a site where lymphocytes are exposed to it (the “depot” effect) and the induction of cytokines, which regulate lymphocyte function. Newer antigen delivery systems such as liposomes and immune-stimulating complexes (ISCOMS) achieve the same purpose by ensuring that antigens trapped in them are delivered to antigen-presenting cells. Bacterial products such as mycobacterial cell walls, endotoxins, etc., are believed to act by stimulating the formation of cytokines. Cytokine induction may be particularly useful in immunocompromised patients, who often fail to respond to normal vaccines. It is hoped that such cytokine induction might also be useful in directing the immune response in the desired direction, e.g., in diseases where only TH1 or TH2 cell responsiveness is wanted (Roitt et al “Immunology,” 4th edition Wolfe Publishing, 1995).
We now provide a new antigen formulation that can tilt the TH1-TH2 balance in favor of a TH1 response. The formulation is useful in immunotherapy, particularly the field of vaccines. It is also useful in studying immune responses and in the production of antibodies.